The present invention relates to air conditioning systems for vehicles and, more particularly, to an air conditioning system for a vehicle, having a heater unit with superior air mixing ability.
In conventional air conditioning systems for vehicles, as disclosed in Japanese Utility Model Publication Nos. 58-32977 and 59-2669, two air mixing dampers are arranged within an air passageway defined within a heater unit and are interlocked with each other to restrict the air passageway, thereby improving air mixing ability.
Further, various techniques have been proposed, in which a fixed air flow deflector is arranged within an air passageway in a heater unit to improve air mixing ability.
In general, the following three basic items (a) through (c) are required for the heater unit:
(a) Reduction in Size
The heater unit is arranged within an instrument panel. Various gages, radio, control switches, harness and the like are concentrated within the instrument panel, so that the interior of the instrument panel is most restricted by space. By this reason, the heater unit is required to be reduced in size.
(b) Air Mixing Ability
The heater unit is provided with a plurality of discharge openings connected, through respective ducts, to air blowing outlets which open to a vehicle compartment, such as defrost (DEF) outlets, ventilation (VENT) outlets, FLOOR outlets and the like. Each duct connected to a corresponding one of the discharge openings is usually divided into two to four branch duct sections which extend to the right and left. Accordingly, if air discharged through each discharge opening of the heater unit is not uniform in temperature, a temperature difference occurs between air passing through the right-hand duct sections and air passing through the left-hand duct sections, so that the air blown toward a passenger on the right-hand side has a different temperature from the air blown toward a passenger on the left-hand side. As a result, a difference in air-conditioning feeling occurs between the passengers on the right- and left-hand sides. The nonuniformity in temperature of the blown air cannot be avoided because hot air of about 80 degrees C and cold air of about 0 degree C are mixed with each other within the heater unit to form air of an appropriate temperature level. However, if the temperature variation of air blown from each discharge opening of the heater unit exceeds 10 degrees C, a practical problem. Thus, the temperature variation of the blown air is required to be within 10 degrees C. The magnitude of the temperature variation variation is called "air mixing ability". A reference to air mixing ability as high means that the temperature variation of the air at each discharge opening of the heater unit is small.
(c) Flow Resistance at Maximum Cooling and Heating
The higher the flow rate at which air is blown from each discharge opening at the maximum cooling and heating, the higher the performance of the air conditioning system. Accordingly, it is required to reduce air flow resistance at the maximum cooling and heating of the heater unit.
However, the above three basic requirements are contrary to each other, and if one of them is improved, the remaining two would be deteriorated.
The air conditioning systems disclosed in the above-mentioned Japanese Utility Model Publication Nos. 58-32977 and 59-2669 do not suggest an air mixing ability that is sufficiently high. In addition, in the above Japanese Utility models, some problems remain unsolved in the reduction of size of the system and in the reduction of flow resistance at maximum cooling and heating.